Phoropters or refractors are instruments that are used in the eye examination process to assist in determining refractive error during what is called subjective examination. That is, where the eye examiner presents various tests and images viewed through the phoropter or refractor to a patient who makes subjective responses to questions asked by the eye examiner. The eye examiner then makes judgment based on the subjective responses of the patient to alter the prescription until a desired refractive prescription is obtained.
Eye examination generally occurs in darkened rooms because the eye chart and other testing images are typically projected onto a screen for viewing by the patient or more recently presented on a computer monitor. At one time, eye examination rooms were typically made about 24 feet long to permit projection of an eye chart or other testing images approximately 20 feet from the eyes of the patient being examined. Twenty feet or six meters is considered to be optical infinity. That is, a distance great enough that a refractive result obtained at optical infinity is insignificantly different from the refractive correction that would be required for viewing objects at actual infinity. More commonly these days, exam rooms are shorter than 24 feet and the patient views an image of the eye chart reflected in mirror at the end of the room, the projected eye chart is actually positioned behind the patient and above their head. Commonly, the eye chart is projected by a projector onto a second mirror that is then reflected back to the back wall of the examination room on a screen which is then viewed by the patient in the first mirror. While some refractors manufactured in recent years incorporate some sort of illumination built into the instrument to aid the Examiner in seeing the settings and registrations of the instrument. The vast majority of refractors presently in use do not include any sort of illumination.
It can be difficult to properly align the patient so that the patient looking through the refractor has their line of sight and that of the refractor directed at the mirror on the far wall of the examination room and properly seeing the eye chart which is presented on the wall behind the patient being examined.
During some kinds of testing done during an eye examination, ultraviolet or deep blue near ultraviolet light is used as an excitation wavelength of light to excite the fluorescence of a chemical substance called fluoroscien. Fluoroscien is a fluorescent dye agent that may be instilled into the eyes in the form of eye drops or by dry filter paper strips impregnated with Fluoroscien in order to assist in the diagnosis of problems with the ocular tear film or increase the visibility of injuries or dry spots on the surface of the eye or ocular adnexa. Fluoroscien may be excited to fluoscence by the application of ultraviolet light from an ultraviolet fluorescent tube or by the direction of high intensity visible light through a cobalt blue filter or by another source of ultraviolet light or near ultraviolet deep blue light.
In a darkened eye examination room, it can be difficult to align the phoropter or refractor so that the patient is looking through it directly at and sees the distant eye chart. This is especially difficult if the patient has poor verbal capabilities. It can also be difficult to view non-illuminated markings or indicia on the phoropter or refractor or other instruments used in the eye examination process.
There still is room for improvement in instrumentation in the eye examination arts.